Heater insulator for indirectly heated cathode



May 10, 1960 R. 1.. KAUFMAN HEATER INSULATOR FOR INDIRECTLY HEATED CATHODE Filed April 25, 1958 5 Sheets-Sheet l 4 iwixlld INVENTOR R. L. KA UF MAN ATTORNEY y 1960 R. 1.. KAUFMAN 2,936,385

HEATER INSULATOR FOR INDIRECTLY HEATED CATHODE Filed April 25, 1958 3 Sheets-Sheet 2 By R.L.KAUFMAN 9? ATTORNEY lllllllllz 'IIIIIIIIII R. L. KAUFMAN May 10, 1960 HEATER INSULATOR FOR INDIRECTLY HEATED CATHODE Filed April 25, 1958 3 Sheets-Sheet 5 INVENTOR RL. KAUFMAN BY ATTORNEY .known heretofore.

HEATER INSULATOR FOR INDIRECTLY HEATED CATHODE Roy L. Kaufman, Allentown, Pa., assignor to Western Electric Company, Incorporated, New York, N.Y., a corporation of New York Application April 25, 1958, Serial No. 730,927

9 Claims. (Cl. 313-340) 'device efliciency and reliability. The specific problem of providing proper insulation for heaters in miniaturized hot cathode devices has proved particularly difficult.

Reduced element size and the attendant necessity for sacrificing structural strength is conducive to the production of heater insulating coatings that are subject to chipping and cracking both during assembly and during life, which in turn produces the obvious difliculties related to the presence of loose bits of heater coating material in the tube envelope. Additionally, the same problems exist in connection with the production of independent heater insulators. Complex and costly production methods and procedures have not provide solutions to these problems.

One general object of this invention is to increase the reliability of electron discharge devices.

More specifically, an object of this invention is to provide a cathode heater insulator combining the advantages of an extremely. high degreeof protection against heater short circuits, and maximum resistance to cracking and chipping.

A further object of this invention is to provide a cathode heater insulator adapted to mass production techniques.

A still further object of this invention is to provide a cathode heater insulator particularly suitable for miniaturized electron discharge devices requiring extraordi-- narily long life. 7

These and other objects of this invention are realized in one specific embodiment comprising a miniature pentode tube generally of the type described in Patent 2,507,706 to R. C. Gee and W. Gronros, May 16, 1950, but specifically for utilization in the repeater devices of underwater cable systems. Although the features of the invention are by no means restricted to employment in tubes of that type, such employment is particularly advantageous in view of the unusually stringent reliability standards required for these tubes. The prohibitive cost of unscheduled tube replacement in underwater repeaters emphasizes the paramount importance of maintaining the highest possible degree of reliability.

The embodiment described in detail later herein comprises a glass envelope pentode amplifier designed for operation in the 1 megacycle range and specifically intended for use with a submarine cable amplifier. A base for all major tube elements is provided by the use of heavy relatively inflexible lead-ins which are headed and fused into the stem. The lead-ins support a top and United States Patent Q Patented May 10, 19.60

are

bottom insulator .plate to "which various tube elements are secured. The cathode is centered in "the tube and comprises two three-sided members joined together in a partially overlapping arrangement to be ofhollow rectangular shape. The heater and insulator assembly are centered in the hollow of the cathode. The control grid structure is a helical wire winding on a frame which is substantially coaxial with the cathode. The screen grid structure is substantially identical to the control grid, is coaxial therewith, and encompasses both the cathode and the control grid. The suppressor grid comprises four rod members symmetrically arranged, two on each side of the screen grid, and parallel to the tube axis.

The anode is a partially cut away box-like member which is substantially coaxial with the cathode screen and control grid structures and which encompasses these elements.

Certain aspects of the cathode heater and insulator assembly in accordance, with my invention should be noted. The heater is a filament, coiled and bent into an M configuration with an insulating coating. The heater insulator is an elongated box-like member with four passages therein to accommodate the four legs of the heater. The two center passages are connected by a narrow slot which is wide enough to receive the center skip section, or uncoiled section, at the bottom center section of the M, but not wide enough to receive the coiled leg. This construction allows the heater to be completely formed and covered with a thin insulating coating prior to assembly with the heater insulator. The otherwise frequently difiicult assembly operation is then accomplished by simply inserting the heater coil into the accommodating passages of the insulator. No risk of bending the heater coil is involved and hence the risk of cracking or chipping the insulating coating is avoided. Moreover, with respect to the cathode itself, the heater .coils are held in an ideal fixed insulated relationship and all possibility of short circuits between the legs of the heater is eliminated.

Conventional, obvious means for meeting the requirements of a heater insulator with an M-shaped heater in no way approach the advantages provided by the features of my invention. For example, a device with four unconnected longitudinal passages therein demands that the heater wire be bent and woven through as a part of the assembly process. Constructing the device as a sectioned member with the two halves meeting along the common center lines of the passages avoids the difficulty of heater bending during assembly but introduces the disadvantages of additional complexity in manufacture 'and the problem of joining the two halves properly during assembly. Additionally, the part of the insulator most subject to chipping and breaking, i.e., the relatively thin Walls between the passages, is largely eliminated in accordance with my invention by the feature of the passage connecting 'slo'ts.

It is to be understood that my invention :is not limited to the M configuration of the heater filament and the number of accommodating passages in the heater insulator disclosed in this specific illustrative embodiment. The principles of my invention encompass any heater filament bent into a zig-zag pattern comprising a plurality of open loops together with a heater insulator made with the requisite plurality of passages therein to accommodate respectively each leg of each loop. Zig-zag, as used herein in reference to heater filament configuration. is meant to include any series of open loops-whethe'r square, sawtooth, serpentine, or of a sinusoidal pattern.

To illustrate further the scope of my invention, we may consider, for example, the case of a heater filament employing four loops, as contrasted to the two loops Dfil'le M employed in the embodiment illustrated herein.

With

four loops the heater insulator,.in accordance with the principles of the invention, would employ a total of eight passages in order to accommodate each of the loop legs. Designating the passages consecutively A through H, it can be seen that a total of three passage-joining slots would be called for, joining respectively passages B and C, D and E, and F and G. Advantages to be gained assesse- P F tionally fused to the stem 1. The dome section 12 of thereby are equally as apparent as in the caseof a heater filament with an M pattern. Each leg is fully insulated from the cathode and from other legs, no bending of the coated heater is required, the insulator itself is of simple construction and readily adapted to mass production techniques, and the assembly of the heater and heater insulator can be accomplished readily with minimum risk of damage to either. I P

Accordingly, the features of my invention include the combination of a coiled M-shaped heater filament having an insulating coating, together with a'heater insulator element comprising an elongated box-like member with four longitudinally extending passages therein to accommodate, respectively, the four legs of the heater. An additional aspect of this feature is that the center two passages are joined by a relatively narrow slot which is adapted to accommodate the uncoiled heater segment at the intersection of the two center legs of the M-shaped heater as the heater coil is slipped into the insulator.

Another feature of my invention is the combination of cathode heater elements comprising a coiled filament with an insulating coating bent into the form of a plurality of zig-zag loops together with a heaterinsulator comprising an integral block of insulating material with a row of passages therein with at least one adjacent pair of the passages being connected substantially throughout their length by a relatively narrow slot and at least one other adjacent pair of the passages being connected substantially throughout their length by an insulating wall portion integral with the block in order to provide a means of entry for the closed end of each heater loop when the heater is inserted into the insulator.

A further feature of my invention is the combination of a heater and heater insulator element, as described in the immediately preceding feature 'set forth hereinabove, together with a hollow cathode comprisingtwo three-sided elements suitably joined together to form the hollow and adapted to accommodate the heater insulator.

A complete understanding of this invention together with additional objects and features will be gained from consideration of the following detailed description and accompanying drawing, in which:

employed as'an embodiment of the invention disclosed herein;

Fig. 2 is a cross-section view of Fig. 1 along the line 2--2,' taken in the direction of the small arrows;

Fig. 3 is a cross-section view of Fig. 2 along the line 33, taken in the direction of the small arrows, illustrating particularly the cathode heater assembly;

Fig. 4 is a cross-section view of Fig. 3 along the line 4 4, taken in the direction of the small arrows;

Fig. 5 is a cross-section view of Fig. '1 along the line 5 5, taken in the direction of the small arrows; and

Fig. 6 is a cutaway perspective view of the cathode and heater assembly. a

Referring now to the drawing, Fig. 1 in particular, it will be noted that the tube envelope comprises a conventional preformed dished stem section or flare 1 having a central exhaust tubulation seal-ofi 2 and a plurality of lead-in wires sealed in a circular boundary around the tubulation seal-01f 2. Identifying the lead-ins, they are the cathode 3, the heater 4 and 8, the suppressor grid 5, the control grid 6, the screen grid 7, and the anode 9. A no-connection lead or anchor 10 is partially embedded in the stem 1 but is not in the circuit, does not extend outside of the stem 1, and serves only as a support member. The body 11 of the envelope is convenjoined together on one side.

the envelope terminates in a top tubulation seal-oft" 13.

A substantially rigid supporting base for all of the major tube elements is achieved by securely anchoring all lead-ins in the stem 1 by means of fusing a glass bead on each lead with the stem. Each of the lead-ins comprises a relatively thin conductor which may be, for example, Dumet metal, which is afiixed, for example by welding, to a relatively heavy conductor such as nickel. With the exception of the control grid lead-in 6, each of the heavy conductors is bent outwardly at approximately a right angle. The glass bead, and consequently the point of seal-in on each lead-in, is located immediately below the joint between the two conductors of each lead-in. Each lead-in passes through a metallic eyelet, for example 14, which comprises a cylindrical body 15, a flange section 16, and two curled tabs 17. A bottom insulator plate 18, formed from a substantially rigid insulating material such as mica for example, is crimped between the head 16 and the curled tabs 17 of each eyelet. Vertical. displacement of the bottom insulator plate 18 is prevented since each eyelet is tack welded to its associated lead-in at two points, for example at points 19 and 20. The bottom insulator plate 18, best seen in Fig. 5, is provided with suitable apertures to accommodate each eyelet together with its associated lead-in 'as well as additional apertures required to accommodate othertube elements. A bottom metallic shield plate 21 is afiixed to the underside of the bottom insulator plate 18 by means of bent tabs 22 and 23. The raised or vertical collar portion 24 of the bottom shield 21, best seen in a Fig. 5, provides shielding between inner grid elernents and the surrounding anode 25.

Anode 25 comprises two flat sections in parallel spaced relation which are joined by strap sections 26,27, 23, and 29. The anode 25, an integral structure, has its ends The ends of the anode 25 comprise two lips 30 and 31 which are bent into juxtaposition and suitably joined together, as by welding, at points 32, 33, and 34 in a mechanically and electrically secure connection. An advantageous mechanical and electrical connection between the anode 2.5 and the anode lead-in 9 is achieved by a pintle hinge-like arrangement with the anode lead-in 9 threaded through accommodating collars formed in the lip 30. The anode 25 is further held in position by extended ears 35, 36, 37, and 38, best seen in Fig. 5, which are bent and clamped to the bottom insulator plate 13. Similar ears 101, 102, 103, 164, and 105, best seen in Fig. 2, secure the top of the anode 25 to the top insulator plate 42, which in construction and function is substantially identical to the bottom insulator plate 18. 7

It will be noted that three lead-ins, namely the anode lead 9 and the heater leads 4 and 8, extend substantially above the bottom insulator plate 18. These three lead-ins pass through eyelets 39, 40, and 41, respectively, which serve to hold the top insulator plate 42 in place in the same manner as set forth hereinbefore in connection with the description of the bottom insulator plate 18. A top metallic shield 43 is afiixed to the top of the top insulator plate 42 by means of crimped ears 44 and 45, and, as in the bottom shield 21, a vertically extending collar 46 serves as a shield between the grids and the anode 25.

Turning now to the grids, the suppressor grid comprises four rod members 47, 47A, 48, and 48A. Two of these, 47 and 48, can be seen in Fig. 1, while opposite end views of each of the four may be seen in Fig. 2 and in Fig. 5. Each suppressor grid rod is suitably joined, as by welding, to a raised tab, for example 49 and 50 on the top shield 43, shown in Fig. l, and to a similar tab, for example 51 and 52 on the bottom shield, shown in Fig. 5. It can also be seen in Fig. 5 that the conducting path between the suppressor grid lead 5 and the suppressor grid rods 47, 48,49, and 50 is effected through an extension 53 of the bottom shield 21, which extension is suitably connected to the suppressor "lead in 5 :at

shows a perspective view of a part of .the screen grid frame 56 behind the side straps 26 and 27 of the anode 25. A top and bottom plan view of the screen grid frame 56 is shown by Figs. 2 and 5 respwtively.

The screen grid advantageously has a gold coating over the screen grid frame 56, the winding 55 and a part of the connecting ribbon 57, which may be of molybdenum and which connects the grid to the screen grid lead-in 7. Such a gold coating may be applied as disclosed in E. J. Walsh Patent 2,549,551, April 17, 1951. The top and bottom of the screen grid frame 56 terminate at each of its four corners in an extending ear or tab. Two of the upper cars, 60 and 61, are shown in Figs. 2 and '3; the second pair of top ears, 58 and 59, may be seen in Fig. 2.

The control grid 62, although smaller, is of substantially the same construction as the screen grid 55. As with the screen grid 55, the control grid 62 is wound upon an open, hollow, rectangular metallic frame 63. The top extending ears, 64, 65, 66, and 67 of the control grid frame 63 may be seen selectively in Fig. 2 and in Fig. 3. Support for both the control grid frame 63 and the screen grid frame 56 is given by the top insulator plate 42 and the bottom insulator plate 18. The body of the control grid frame 63 and the body of the screen grid frame 56 are contained between insulator plates 42 and 18, except for the end ears which protrude through suitably aligned apertures in the insulator plates 42 and 18. See, for example, Fig. 3. The control grid frame 63 and winding 62 is also coated with gold as disclosed in the above mentioned Walsh patent. A conducting path between the control grid 62 and the control grid lead-in-6 is provided by a conducting ribbon 68, as shown in Fig. 5.

The cathode 69, which is encompassed by both the control grid winding 62 and by the screen grid winding 55 comprises two three-sided members 76 and 71, best seen in Figs. 4 and 6, suitably coated, for example, with a conventional spray coating of barium strontium carbonate 74 and fitted together to form a hollow rectangular box. To create an effective bond between the over lapping portions of the two sides 70 and 71 of the oathode 69, a method devised by E. J. Walsh of the Bell Telephone Laboratories and known as diffusion welding 'may advantageously be employed. Prior to effecting the bond, a conducting ribbon, nilvar for example, is inserted between the overlapping end sections, as at 72 and 73 in Fig. 6. The application of pressure of the order of 1300 pounds per square inch combined with temperature of the order of 700 C. is employed in the bonding process. An unusually strong bond is created and the obvious disadvantages inherent in the welding of miniature parts are avoided. The conducting ribbons inserted between the overlapping end sections of the cathode 69 serve the same purpose as a welding bead in a conventional weld. After the bond is completed, the ribbon on one side is trimmed off at both ends while the ribbon on the opposite side is trimmed only at one end. The untrimmed end 79 serves as the conducting path between the cathode 69 and the cathode lead-in 3, as shown in Fig. 5. The cathode 69 is effectively retained between the top insulator plate 42 and the bottom insulator plate 14 by embossed projections 75, 76, 77, and 78, shown in Fig. 6, which bear respectively against the top and bottom insulator plates.

The cathode heater filament 80, best seen in Fig. 6, is relatively tightly coiled and bent into an M or W configuration. The short segments 81, 82, and 83 at rthe intersections of the heater legs are not -.coiled. :Some

appreciation of the close :tolerances and the degree of miniaturization involved in the cathodeheatertassembly will be realized when some of the dimensions are lCOIl" sidered. Forexample, the uncoiledsections 81, .82, and 33 shown in Fig. 6 are 1.5 millimeter in length. The

coil comprises 156 turns per inch and the space between -coils is 1 millimeter.

After the cathode heater wire is coiled and bent into the desired configuration, .it is sprayed with aninsulating coating, aluminum oxide for example, except for a *relatively :short section at each terminal end which .is .left bare. *It will be understood that any considerable bending .of the heater filament after the insulating coating is applied would necessarily involve the :risk of cracking or chipping the coating.

The .heater insulator 87, best shown in Fig. 6, is a rectangular box-like member with a row offour passages therein, 88, 89, :90 and 91. It may be formed, advantageously, from .a refractory insulating material, aluminum oxide for example. The passages are .of suitable size to accommodate, respectively, each ofthe four coated heater legs. An accurate fit is desirable since the heater filament 80 should be inserted into its insulator 87 without forcing. At the same time, the fit should be sufiiciently snug so that the possibility of movement or vibration of the heater legs in their accommodating passages is substantiallyeliminated. From Fig. 4 and from .Fig. 6 .it can be seen that thetwo center passages 89 and in the heater insulator 87 are connected throughout their length 'by a relatively narrow slot 92. The slot is sufiiciently wide to accommodate the uncoiled heater segment 82 as the heater is inserted :into the insulator. ever, to ensure that no contact between the two center legs of the heater will occur. It may be:noted in 'Fig. .6 that :the heater 80 and its insulator 87 may be assembled only in one direction, i.e., by slipping the heater coil in at the bottom of the insulator. Insertion of the heater filament beyond the desired point is prevented by loops 81 and 83 coming in contact with the solid insulating walls existing between each of the outer passages and its respective adjacent inner passage.

In order to give the heater filament additional rigidity and strength at the terminal connecting points, a mandrel member 84, best seen in Fig. 3, is inserted in each terminal end :of the coil 80 after the coil '80 has been inserted into the insulator 87. Additionally, a conducting sleeve 85 and 86 is slipped over .each coil terminal. Each sleeve 85 and 86 is then crimped to the coil and a spot weld is .applied on each in order to bond together the sleeve 85, 86, the mandrel 84, and the heater coil 80.

Conducting paths between the heater terminals 93 and .94 and the heater leads 4 and 8 are provided by conducting ribbons 95 and 96 which are suitably joined, as by welding, to extended heater leads '4 and 8 respectively and to the sleeves 85 and 86 which have been crimped and welded to the heater terminals.

Mounted on extended heater lead-ins 4 and 8 respectively are flash-getter supports 97 and 98, shown in Fig. .1, which in turn support respectively active getter bars 99 :and 100. The getters are of conventional commercial design, comprising for example a barium and iron composition, and are flashed by coupling with an exter- 1121 high frequency energy source.

It is to be understood that the above-described embodiment is intended to be merely illustrative of the principles of the invention. Numerous other arrangements may be devised by persons skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. In an electron discharge device having a hollow cathode and a heater element therefor, said heater element comprising four parallel legs in juxtaposition in the same plane with a pair of adjacent ends of the two The slot .92 is sufliciently :restricted, how

center legs being connected together andthe'opposite ends thereof each being connected respectively to the end of the outer leg adjacent thereto, means for maining a first longitudinally extending passage therein for receiving one outer leg of the heater, a second longitudinally extending passage therein for receiving the other outer leg of the heater, third and fourth longitudinally extending passages therein for receiving the two center legs of the heater, and a restricted passage connecting said third and fourth passages throughout their length for receiving the portion of the heater connecting the two center legs whereby the heater legs are maintained in fixed space relation upon insertion into said member.

2. In combination in an electron discharge device a cathode heater comprising a coiled filament with an insulating coating thereon, said filament comprising four parallel legs in juxtaposition in the same plane with a pair of adjacent ends of the two center legs being connected together and the opposite ends thereof each being connected respectively to the end of the outer leg adjacent thereto, and a heater insulator comprising an elongated integral block member having a row of four longitudinally extending passages therein, the two center passages in said row being interconnectedthroughout their length by a relatively narrow slot, said slot being adapted to receive a short uncoiled section or" said filament at the intersection of the two center filament legs upon insertion of said filament into said insulator.

3. The combination in accordance with claim 2 wherein said insulating coating and said insulator are alumina.

4-. In an electron discharge device employing a hollow cathode and a heater filament in fixed insulated relationship to the interior of said cathode, said filament comprising four parallel legs in juxtaposition along a single plane with a pair of adjacent: ends ofthe two center legs being connected together and the opposite ends thereof each being connected respectively to theend of the outer leg adjacent thereto, first insulating means between said filament and said cathode and second insulating means between said filament and said cathode, said first insulating means comprising an insulating coating on said filament, and said second insulating means comprising an integral block insulator having a row of four holes therein, each hole adapted to receive, respectively, one leg of said filament, and a relatively narrow slot connecting the two center holes of said row throughout their length, said slot being adapted to accommodate the central bottom portion of said filament when said filament is inserted into said insulator.

5. In an electron discharge device, in combination, a hollow cathode element, a heater filament adapted for insertion into the hollow of said cathode, and first and second means insulating said heater from said cathode,

said heater filament comprising a plurality of coiled legs in juxtaposition, two adjacent ends of at least one pair of legs being connected together with the other ends of said pair of legs being connected to the ends of difierent legs respectively adjacent thereto for forming a single continuous conductive path, said first insulating means comprising an insulating coating on saidheate'r filament and said second insulating means comprising an insulator block adapted totmaintain said heater in fixed insulated relationship to the interior of said cathode, said block having a plurality of passages. therein each adapted to accommodate, respectively, a leg of said filament, alternate adjacent passage pairs being connected by a relatively narrow slot, each of said slots being adapted to receive, respectively, a short wire section connecting at least one pair of said filament legs upon insertion of said filament into said second heater insulator means.

6. An electron discharge device in accordancewith claim 5 wherein said first and second insulating means comprise alumina.

7. In combination in an electron discharge device, a cathode heater element and insulating means therefor, said heater element comprising a coiled filament bent into a plurality of parallel legs in juxtaposition, two adjacent ends of at least one pair of legs being'connected together with the other ends of said pair of legs being connected tothe ends of difierent legs respectively adjacent thereto to form a single continuous conductive path, said insulating means comprising an insulating coating, and said insulating means further comprising an elongated integral insulator block having a row of longitudinal passages therein, each of said passages being adapted to accommodate, respectively, one of said filament legs, a relatively narrow longitudinal slot connecting at least one pair of said passages substantially throughout their length whereby the connected ends of all of said filament legs on the end of said filament comprising the lesser number of connected legs are accommodated upon insertion of said filament into said insulator block.

8. In an electron discharge device in combination, a cathode heater comprising acoiled filament bent into a plurality of parallel legs in juxtaposition, two adjacent ends of at least one pair of legs being connected together by an uncoiled filament section with the other ends of said pair of legs being connected to the ends of difierent legs respectively adjacent thereto by uncoiled filament sections to form a single continuous conductive path, and an integral block insulator with a plurality of longitudinal passages therein, at least one adjacent pair of said passages being connected substantially throughout their length by a relatively narrow slot and at least one other adjacent pair of said passages being connected substantially throughout their length by an insulating wall portion integral with said block, whereby said filament may be inserted into said insulator.

9. A combination in accordance with claim 8 wherein a metallic mandrel member is inserted into each terminal end of said coiled heater filament and wherein each of said coiled terminal ends is enclosed by a metallic sleeve member.

References Cited in the file of this patent UNlTED STATES PATENTS Veazie Nov. 22, 1949 Wheeler Mar. 18, 1952 

